1. Field of the Invention
The present invention relates to a microorganism which degrades nitrosamines formed in tobacco leaves during the curing and storage processes of the tobacco leaves, and a method of reducing nitrosamines formed in tobacco leaves during the curing process and/or storage process thereof, by using the microorganism.
2. Description of the Related Art
Nitrosamines contained in tobacco leaves (Tobacco Specific Nitrosamines, which will be referred to as “TSNA” hereinafter), are not present in tobacco leaves immediately after harvesting (i.e., green leaves), but formed during the curing process and storage process thereafter by a reaction between alkaloids and nitrite contained in the tobacco leaves. This nitrite is formed by a microorganism which is present at the surface of the tobacco leaf and which has the capability to reduce nitrate.
The main TSNA formed in the curing process and the subsequent storage process are N′-nitrosonornicotine (which will be referred to as “NNN” hereinafter), 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (which will be referred to as “NNK” hereinafter), N′-nitrosoanatabine (which will be referred to as “NAT” hereinafter), N′-nitrosoanabasine (which will be referred to as “NAB” hereinafter), and the like.
Examples of the method which has been conventionally known as a method of reducing the content of TSNA in tobacco leaves include: (1) a method of suppressing formation of TSNA; and (2) a method of removing TSNA which has been formed.
Examples of the method of suppressing formation of TSNA include: a method of decreasing the content of alkaloids in tobacco leaves by reducing the amount of nitrogenous fertilizer; a method of reducing TSNA formed during the curing process, by adopting an indirect-heating type of curing barn in place of a direct-heating type of curing barn (this method is employed mainly for flue-cured tobacco); a method of breeding a new tobacco varieties having less alkaloid content, which method relies on progress of the breeding technology; and the like.
Further, a method has recently been reported in which formation of TSNA is suppressed by microwave irradiation (PCT National Publication No. 2001-503247). However, such rapid drying and curing as caused by the aforementioned treatment with microwaves results in insufficient change in the type of components of the tobacco leaves, which change would be effected in a satisfactory manner in the conventional curing process. Thereby, the resulting tobacco leaves which have been cured more rapidly than by the conventional method exhibits poor flavor and taste when smoked.
In the case of the method of removing TSNA (thus formed) from tobacco leaves, the number of reported examples thereof is smaller than the method of suppressing formation of TSNA. As one of these examples, a method is known in which TSNA is removed from tobacco leaves by supercritical extraction (WO 01/65954). However, this method has not been put to practical use in terms of the cost thereof.
Due to the above-described circumstances, there has been a demand for a novel method of reducing the content of TSNA which is known to be formed during the curing and storage processes of tobacco leaves.
Further, there has been a demand for tobacco leaves, as the raw material of cigarettes, which have relatively less content of TSNA and maintain good flavor and taste satisfactory to consumers.
Accordingly, the object of the present invention is to provide a method which enables reducing the content of TSNA formed during the conventional curing and storage processes.
Additionally, it is already known that a micro-organism belonging to genus Aspergillus which is a filamentous fungus isolated from unrefined soy source degrades nitrosamines (Jpn. Pat. Appln. KOKAI Publication No. 10-276681). However, it has been pointed out that microorganisms which belong to genus Aspergillus need high moisture content for survival, which high moisture content may cause adverse effects on the quality of tobacco leaves, especially on the flavor and taste thereof. Therefore, use of such a microorganism as described above in the treatment of tobacco leaves may cause a problem in tobacco quality.